The invention relates to a drum as axle in a brush roller. Brush rollers are used for cleaning large flat surfaces and also in industrial context for deburring, polishing or roughening surfaces or edges.
It is well known that axles for brush rollers, particularly brush rollers used in road cleaning machines, are difficult to manufacture. These brushes generally have a length of between 1.5 to 4 meter and a diameter of between 700 and 1800 mm. The brushes rotate at a speed of between 400 and 1000 r/m.
The traditional method of manufacturing the axle of a brush roller is to attach axial holders on a steel pipe or rod, at the periphery of the pipe. Various types of brush magazines are then fitted in these holders. These axial holders are generally made of extruded aluminium. Other components included in such a brush roller are various forms of key joints and spacers. The steel pipe and spacers are welded together with known precision. A large number of holes for attachment bolts must also be drilled and threaded in the steel pipe. This vast number of components entails high storage costs for material as well as expensive machining costs.
Commercial alternatives available are to design the axle of the brush roller as a fully extruded aluminium section. One problem is that the die used for the extrusion is limited as to size so that only certain maximum diameters can be produced. Furthermore, these extruded aluminium sections are extremely heavy since the material is thick, and it is impossible to reduce their mass by inserting cavities. A considerable drawback when extruding aluminium sections is the banana shape the section acquires on the cooling bed. A section that is 4 meter in length may have a curvature of 4 mm or more. This curvature entails extra work at the dynamic balancing.
It is also known through U.S. Pat. No. 3,134,123 and U.S. Pat. No. 3,862,463 to make the cylindrical axle of the brush roller in segments, which are joined together and anchored, to hub members situated centrally at the ends of the axle. The segments are in the form of thin-walled sections, which are not reinforced in axial direction, and the axle is therefore limited in both length and diameter. This method of constructing the axle of a brush roller does not permit the manufacture of long axles, e.g. 4 m, nor axles having large diameter, e.g. 1200 mm, because of the unbalance occurring at the revolution speeds involved. U.S. Pat. No. 3,134,123 also indicates that the embodiment shown in FIG. 3 constitutes a self-supporting construction. However, this construction is extremely expensive since the dovetail joints of the sections cannot be manufactured without after-working, with the tolerances necessary if the joints are to be free from play. Furthermore, the dovetail form according to U.S. Pat. No. 3,134,123 must have a certain play to enable one section to be axially inserted into another section, and this per se results in play in the construction.
The object of the invention is to solve the problems mentioned above and to improve a drum in the axle of a brush roller so that the axle becomes simpler and less expensive to manufacture, as well as being lighter, which contributes to increased stability at the bearing housings of the axle.
Another object of the invention is to provide a drum for the axle of a brush roller which drum, under dynamic loading, behaves as a rigid cylinder.
A further object of the invention is to provide a drum for a brush roller with relatively large diameter and length, which can be produced from extruded aluminium sections and which, after assembly, performs entirely free from play and with a rigidity equivalent to a homogenous body, e.g. a cylinder.
The objects stated above are achieved and the drawbacks eliminated by means of the present invention as defined in the claims.
The method for assembling a drum according to the inventive concept is that the drum forms a part of an axle and that the axle constitutes a part of a brush roller. Characteristic of the assembly is that an axle consists of a drum on which an end plate with two shaft ends have been mounted.
The drum preferably has circular cross section. A plurality of axial, preferably U-shaped channels are arranged at the periphery of the drum. A normal axle has 16 channels but the number of channels may be either more or fewer. The drum is preferably made from four segments of extrude aluminium sections.
The number of segments is in no way limited to these four segments but may vary from two or more, e.g. 2, 4, 6 or 8. An even number of sections is preferable in order to achieve dynamic balance in the simplest manner at rotation. The segments exhibit an outer arc shape. Four segments, for instance, are fitted together to form a drum. Each segment has a first edge part with a first shoulder and a second edge part with a second shoulder.
Assembly of four segment sections to a drum is as follows:
In a first step each segment is arranged so that the edge portion of the first shoulder and/or the edge portion of the second shoulder are in contact with the second or first contact surface, respectively, of an adjacent segment. This ensures that the drum will always have the same diameter. A space between the various segments may cause unbalance. The contact surfaces between the shoulders of the segments are flat so as to obtain the greatest possible contact area without having to machine the surfaces. Alternatively the contact surfaces of the shoulders may be provided with pins and recesses in order to a greater extent to take up tangential shear stress between the segments.
A variant of the shape of the segments is to arrange two adjacent segments with the lower side of the second shoulder of a first segment in contact with the upper side of the first shoulder of a second segment.
This is done when the shoulders of the segments are at different levels, i.e. radial distance from the axis of rotation of the axle. An alternative embodiment is the use of two differently shaped segments, alternate segments being identical, i.e. the shoulders on alternate segments are at equal radial distance from the inner arc.
Another factor is that each section is curved at the extrusion. By dividing the drum into segments, the curvature of the segments will be compensated and the drum becomes straight. At one and the same extrusion process each rod will be cooled in the same way and each will acquire similar defects.
A second step entails drilling or drilling and threading through-holes in radial direction, e.g. through the first, outermost shoulder as a clearance hole and through the second, innermost shoulder as a threaded hole, in each segment. Two or more holes are drilled along the segments in each shoulder, at equal or different distances from each other.
The third step entails passing an attachment element, a bolt or a screw and nut, through each hole. This screw joint ensures complete freedom from play, which is necessary if a brush roller 2.5-6.0 meter in length is to be balanced dynamically and then withstand a continuous speed of revolution of up to 1200 rpm.
When the drum is mounted on the axle, a circular plate with a concentrically arranged shaft end is fitted on the end portions of the drum. Congruence exists between every or every other segment incorporated in a drum. The advantage of having only one shape for the segments in the drum is to save costs.
The segments incorporated in a drum exhibit the following characteristics:
the segments consist of extruded aluminium sections;
a segment exhibits an outer arc form;
each aluminium section is provided on its upper side with two or more, preferably four, radially protruding beams;
a U-shaped channel is formed between two adjacent beams;
each segment has a first shoulder and a second shoulder.
In one embodiment the upper side of the first shoulder and the lower side of the second shoulder of a segment preferably have flat surfaces.
The segments are also made double-walled, one or more cavities being formed in each segment. In a segment with two cavities, these cavities are separated by radially reinforced spacers extending axially along the entire length of the segment. The U-shaped channels of the segment are also situated radially in relation to the imagined central axis of the drum.